1. Technical Field
This invention relates to a method of inspecting a magnetic recording medium typified by a hard disk drive, especially to a method which is suitable for certification testing adopted in the inspecting method, and further to a process for producing a magnetic recording medium utilizing the inspection method. Further, the invention relates to a method of controlling the movement of a magnetic head in a magnetic recording/reproducing apparatus, and to a magnetic recording/reproducing apparatus having a magnetic head capable of moving in a controlled manner.
2. Description of the Related Art
Magnetic recording devices typified by a hard disk drive are widely used as external memory units of information processing devices such as computers. In recent years magnetic recording devices have also been used as video recording devices for animated images.
Hard disk drives are ordinarily provided with (i) a shaft around which a magnetic recording medium disk having a doughnut shape with a center opening is rotated or a stack of the superposed magnetic recording medium disks are concentrically and synchronously rotated; (ii) a motor which is coupled via bearings to the shaft for rotating the magnetic recording medium disk or disks around the shaft; (iii) magnetic heads for recording and reproducing information on both surfaces of each magnetic recording disk; (iv) supporting arms to which the magnetic heads are attached; and (v) a head stack assembly which is capable of synchronously moving the supporting arms for moving the magnetic heads to the desired positions on each magnetic recording medium disk. The magnetic heads for reproducing information are usually floating-type heads moving at a certain floating height on the magnetic recording/reproducing medium disk.
Generally magnetic recording mediums provided in a hard disk drive have recording regions in a plurality of concentric tracks each extending in the peripheral direction and arranged in the radial direction, and sub-recording regions called sectors which are sub-divisions of each sector. The recording of information in a magnetic recording disk is generally conducted in track units and sector units.
A magnetic recording medium is ordinarily produced by a process comprising forming a primer layer, a magnetic layer, a protective overcoat and a lubricating layer by sputtering in this order on a substrate made of, for example, an aluminum alloy or glass. The thus-produced magnetic recording medium is subjected to a glide test and a certification test in turn.
The glide test is a test for determining the smoothness of a surface of the disk, i.e., for determining the presence of protrusions on a surface of the disk. If protrusions having a height larger than the floating height of magnetic heads (i.e., a distance between the disk surface and the magnetic heads) are present on the surface of a magnetic recording medium disk, the magnetic heads strike the protrusions at recording and reproducing, which causes damage of the magnetic heads and often gives defective magnetic recording mediums. The glide test is a test for determining the presence of such protrusions on the magnetic recording medium (see, for example, JP H01-260014A).
A certification test is conducted on magnetic recording mediums which have passed the glide test. That is, in the certification test, as with the recording and reproduction of ordinary hard disk drives, prescribed signals are recorded on a magnetic recording medium with magnetic heads, after which the signals are reproduced, and the reproduced signals are examined to determine the electrical characteristics of the magnetic recording mediums and the presence of defects thereof whereby quality of the magnetic recording mediums is evaluated (see, for example, JP2003-257016A).
As a certification test, a method of utilizing signals derived from thermal asperities from an inspection head with a thermally sensitive element has been proposed (see, for example, JP H10-105908A)
Servo information is written by using a device called servo-writer into a magnetic recording medium which has passed the certification test. Then the magnetic recording medium is installed in a hard disk drive. As a magnetic head for use in the hard disk drive, a magneto resistive head (i.e., MR head) has been proposed. With an increase in recording density of the magnetic recording medium, a floating height (i.e., distance between the head and the magnetic recording medium) of the MR head becomes smaller.
Due to the fact that a floating height of the MR head becomes smaller with an increase in recording density of the magnetic recording medium, as mentioned above, the MR head readily impinges against minute protrusions which are inevitably present on a surface of the magnetic recording medium, and thus the head is easily abraded with the result that troubles such as output reduction and deterioration of characteristics are often caused by abrasion of an element of the MR head. Since the minute protrusions have a very small size, a substantial long period of time is required to overcome such troubles and to put into the market a new type of magnetic recording medium having improved characteristics. Further, the troubles caused by abrasion of the head element occurring due to the minute protrusions results in the reduction in the reliability of a hard disk drive.